Surround audio systems used in movie theatres and home cinema systems use multiple speakers to simulate a sound field surrounding the listener. Surround audio greatly enhances the listener's experience. Currently, one of the most popular surround audio configurations is the well-known surround 5.1 configuration which uses five full bandwidth channels and a low frequency effect (LFE) channel. The most popular format for storing high quality music, however, remains two-channel stereo, not surround. Therefore, for the most part, high quality music cannot be enjoyed in surround.
Upmixing processes may be applied to audio signals to derive additional audio channels, for example, to go from two-channel stereo to surround 5.1. Existing upmixing methods create an allusion of surround sound through the use of matrixing, phasing, time delay, and reverberation effects added to the stereo mix as a way to generate surround. While these conventional systems and methods create an effect, they also produce unnatural-sounding artifacts that may cause music to sound fake, hollow, or annoying to the listener. The listener may experience a loss of overall clarity or quality as if “something just does not sound correct” with the sound. There may be little or no distinction to the segments in the conventional upmixed surround presentation. These issues diminish the listener's experience.
Another area in which sonic artifacts negatively affect the listener's experience is peak limiting. Peak limiters have become ubiquitous in music production. With the advent of digital processing, peak limiters can react instantaneously to or even in advance of audio peaks, ensuring that the signal never gets louder than a predetermined ceiling. Conventional peak limiters, however, come at the cost of clarity and punch, and added spectral artifacts. Thus, conventional peak limiters may do a good job at limiting peaks but they add harmonic spectra that disturbs the sound. These issues also diminish the listener's experience.